My summary:1/ You need strong vibration to compact it, and you need to tune the frequency to the mold. A concrete vibrator on a VFD works well, but needs to be well bolted to the mold. Clamps just fall off.2/ I used Thomas Zietz's Spreadsheet for the recipe, as I couldn't get SILIMIX 282 graded aggregate. It is now available for a decent price from this web vender in Germany.http://www.moertelshop.com/SILIMIX-282-guenstig-kaufen4/ If you make your own recipe, the finest fine needs to be a super fine powder, and the largest aggregate needs to be about 1/5 of the thinnest section. Fine play sand is too course to be the finest part of the mix. It is the second aggregate in mine. 5/ I used a cheap casting epoxy off Ebay.de. The lower viscosity the better. I use 8% epoxy. The mix is very dry. I put too much in the mold before starting to vibrate, and didn't get all bubbles out. Next time I will use vibration from the start, before adding E/G.6/ This stuff sticks like **** to a blanket. I waxed my mold, but the wax just gets abraded off. Coating the mold in brown packing tape makes for an easy release though.

Tensile and compressive strength is largely irrelevant for a machine base. Stiffness, damping then stability are the main figures of merit , and they are dependent on the youngs modulus and inherent damping and aging characteristics of the material. The advantage of E/G, is that it has fantastic damping, far better than cast iron. Once cured it is very stable (Concrete keeps shrinking for years). As it is a cold casting process with insignificant shrinkage, you can cast sharp corners, thick sections, big changes in thickness etc which would rip an iron casting apart during cooling. It has a quite low youngs modulus, but you just achieve your target stiffness by making thicker sections.

How do you think I should approach if I want to make a "cross slide" to this one out of mineral casting? I need to get two set of rails X and Y. X on bottom and Y on top. These axis are square to each others, about 50 mm apart (thickness) and on parallel planes. Something like 350*200 area, maybe 3,5 litres of volume, maybe scale up to 10 litres and that would weight something like 8-23 kg? Does it sounds completely bonkers for first project on epoxyconcrete?

I was thinking of using key-stock (or pre machined bar) that comes proud of surface few millimeters to allow machining them straight for rails/gibs. Accurately ground spacers between them to ensure top and bottom are reasonably parallel during curing. Just need small reasonably straight plate as a form bottom to make everything reasonably straight.

If I understand form making, pretty much no no traditional release agent works? You said that packing tape works. Hmm. maybe a self adhesive PVC film would work too?

I used cheap brown packing tape on my test mold, and it releases well. Problem you have with larger parts is that you need very little adhesion, to give a huge removal force required over the large surface, and you have a rigid lump. The guying doing E/G professionally on the CNCEcke consider a wooden mold sacrificial. They use coated printers Multiplex (Siebdruckplatte), but still have to destroy it to demold. Fro the permanent steel molds, they designed in threaded features to break the mold, and say enormous force is necessary.

That sounds like a very doable sized first project. I mixed up about 10kg of E/G in two batches. Using a mixer/swirler on a normal electric hand drill, more than about 5kg per batch gets pretty difficult to get the largest aggregate wetted. A normal concrete mixer would be useless. The stuff is too dry, and would just stick to the sides and spin around. At least with the epoxy I used, you have plenty of time. I think it had about 4H till it jelled. Once the aggregates are added, there is so much mass, that you don have to worry about the epoxy heating itself up.

I got too complicated with trying to add rebar. Unnecessary. As you suggest, steel strips bolted in routed slots in the bottom of the mold, sealed with silicon, spacers attached to hold the top rails/pads in place during casting. One it is all cured (Thomas suggested I leave it a week before demolding) mill/grind/scrape the surfaces parallel, drill and tap the attachment holes.

I have only ever seen threads of people who were semi successful at making grinding sleds. With 0.4mm to remove, grinding is not a hogging process.

I believe nothing sticks to HDPE (?) aka trash bags and or "elmukelmu" kitchen plastic wrap.Aka plastic builders tarp also, I think.The thin wrap would probably stick to crevices and chemical/mechanical means would be needed to take it off, if you need t.

I made some concrete bits 10 years back.The 7x minilathe lathe bed was a huge technical success. 9.5/10.

I made the mild steel box, flats are on side, 120 mm tall/thick, 900 mm long, 700 mm deep.2 sets of 3 rebar, inside, crossed, welded onto one side only of box, at end and at front, wleded at center onto heat other.Box is finish welded. Cool.

Then heat rebar with propane torch for 10 mins or so. Now weld last 2 ends of rebar, back side on x axis and left side on z axis. Leave propane torch on, in middle, 3 mins == till welds cool.Take off torch.Leave to cool.The cooling rebar is an enormous spring, and the hole box is really tight, with very heavy (== 5-10 metric tons, by my estimate) preload.

Flip on old tabletop, with flat plastic melamine (does not stick to concrete).Leave granite 40x40 flooplate at bottom, to be catch pan, dropped == 20 mm from center to collect swarf.I made a hole in middle, and left a plastic tube through box, to allow liquids aka coolant/oil to leak out, == 15 mm.

Lathe was flat mounted, very rigidly, onto the steel box, before concrete.I used 2 sets of flat legs, in x axis, ie 2 flats at HS, 2 at TS.120x70x12 mm, one on top of the the other. Bolted SHCS, 6 mm.

How to get lathe to be flat.When the lathe was flat, mounted to top legs rigidly (bolted), but top legs are floating, ie not mounted to anything.The legs align the top plate, HS end, since its not fixed at all.

The bottom flat plate, same 120x70x12 mm (xyz) is now bolted onto the top flat (previously drill &t through both at same time).Now, the bottom plate is bolted, perfectly flat, onto top plate.As the 2 legs together are far apart, ie contact points are 700 mm between front end x++ and back end x--, now spot weld bottom plate only, onto frame, ie the steel box. From below, only. Onto bottom flat, only.

The spot welding is really small, and the thermal mass is so large of legs and frame, it cannot move or twist anything.Then add a few more spots, and unbolt top plate, and lathe.The two flats will always get maybe 0.01 mm or better registration, one on top of another.6 mm shcs == 240 kgf (2400 N) x 4 and easily bends the 12 mm thick plates flat one onto the other, in step one.

Hanermo: Thank you very much. Some places picture or drawing or any kind of illustration would have helped. Part I got, part I got lost, I'm that fluent on mechanical construction. My first <60 kg lathe was bolted on 30 mm hot rolled steel plate. It did help great deal.

Another challenge with a grinding sled running on the lathes ways, is that there is no overtravel, so you are left with unground bits, so you need to design you sled to allow for that.

Mark

I have seen those bits. I'm sure he used unworn ways (or parts of ways) like tail stock way is pretty much always intact near head stock -and vice versa.

What I did not like on that setup is small grinding stone and I didn't see any calibration of the stone face with diamond. That contraption does not oscillate....how did he stop it from producing stripes?

Furthermore my problem with mill ways is that there are no unaffected ways left....least not on same axis.

Table is the longest item, it has 1000mm of guide ways - dove tail type. I asked around and 500 mm would have been easy on table size, but 1 m is bit long for any of my friends. And then there is then knee, it does not fit on normal milling machine.

I have been checking the dimensions and the knee is awkward. Then there are the flat upright square ways, about 1000 mm long on the milling machine frame. Plan is to measure first to see how much and where wear is, before doing anything on it.

Anyway, most wear is on the table x-axis and that is most challenging: longest, most wear, dove tail and even if I pull it off, I still have to refit the screw.

How about milling out pockets in sections on a smaller mill, to get the necessary depth for Moglice? Moglice wont care if the bottom of the pockets have steps, and this way you can keep the screw centerline.

How about milling out pockets in sections on a smaller mill, to get the necessary depth for Moglice? Moglice wont care if the bottom of the pockets have steps, and this way you can keep the screw centerline.

If the Knee is not as badly worn, just scrape it.

Mark

That is like plan B vs, scrapping it. I don't like moglice, because I don't know what it is how it works. Makes me feel iffy.

Is't it stuff that has big part epoxy, some solvent and then some lubricants like MOS, graphite and some metalic bearing material like coppermetals and maybe teflon?

Solvent makes it shrink and deform a little, metalic particles need oil lubrication and teflon - I don't get it.

Logical step would have something like that to cast over epoxyconcrete. And it looks like it has been considered. Even googled recepies of home made moglice type castable bearing material. It's distracion in it's own right.

Hanermo: Where you got that "elmukelmu"? It's Finnish for a cling film wrap. Not very international word. You got me thinking that I have seen very nice surface quality on samples poured into a disposable plastic cup. Those are made out of PET, PP or PS. Probably more. PP and PET family seems to be difficult to glue with epoxy and therefore pretty nice material to prevent polymer casting from gluing into mould.

You could also solve it easily, and for maybe 200€, in one hour (or even less, depends).

Contact Grönbloms, the local HFO or Haas rep for Finland.Ask, from sales, for a recommendation to one of their clients with a HAASF VF5 or bigger, who would be happy to do a small one off job, and plane the ways.

They are nice guys, and are ime, imho, always happy to recommend clients who will/can do work like this.Ie recommend a machine shop that is happy to work with one private individual, on a one-off, and who has a big enough machine, with 1 m+ table travel.

The machine shops tend to do these jobs in between, or on slack time, and if you are not in a big hurry they can do this cheaply.They also get favourable publicity, and this tends to bring in more work, later, and good word of mouth.

A single pass with a suitable cutter should leave the ways within 0.01 mm or so, overall.

It's not even nearly DIY...but when I'll take it appart I'll might change my mind. Specially if it turns out that I have whole lot less than 12 surfaces to plane.

Today I checked 20*20 mm and 22*14 mm keystock. Unbelievable straight. All of them had a bow, max. 0.05 mm / m, about the same than linear bearings. That sort of bow straighten easy with finger pressure. Unbelivable luck. Would need superstructure and where it would be easy to bolt down.

I cannot, easily enough, make the assy to much better than 0.01 mm (this level is easy. Assemble so cars don´t bind, by hand. Shim as needed)).The geometric averaging makes the actual accuracy be about 2-4x better.

Similar to modern medium VMCs with 1-1.5 m table travels (they do 25 kW).

X axis is the long one, 2200 mm long end-end with 1600 free travel.Beams are 2200x20x200 mm, with 35 mm rail on top, for 235 mm total height.Over 1600 mm free span, a 235 mm flat steel beam, 2 of, can probably carry way more than 50 metric tons without failure, in theory.(Its actually not on top of the beam, but..)

Huh! That is a big plan. Very nice to read on how differently people approach different problems. Hope to hear more from that project progress.

I have been doodeling on paper some spindle designs. Goal is to make a simple spindle that will allow a little of axial and radial grinding.

Basically I need a fixed bearing near grinding stone and free bearing near pulley at the other end of the shaft.

I considered first classical pair of angular contact bearings, but very few are offered with any dust shields. I'm setling on dual angular contact bearing with 2RS shields, this I might just get away with the loading and RPM I need here.

I draw two slightly different basic designs, which one is prefered and why?

Is there better, easy to make design?

* Addition: The square on very left is a polyvee belt pulley - free bearing end - ball bearing. Grinding stone will be on right hand side (not drawn) on locating bearing side.....just to clarify my doodle.

Does a surface grinder really need the thrust control of paired AC bearings? My Clarkson T&C grinder only has deep groove ball bearings. Since you are grinding a surface, with no precise shoulders, I'd think you only need radial stiffness, and could make the spindle more simple.

Flat surfaces and there would be no problem with deep groove ball bearings. Or even with bench grinder that was suggested before and I did consider it.

However: I have dove tails to grind too and they probably will not be done in one go. Another sightly problematic surface is back of the vertical. only way I can imagine reasonable size grinding wheel there is a cup/face type wheel in reverse. I.E. I might need radial and axial loading in both ways. I tried to resist the latest one, because othervice I could have got away with two opposing angular contact bearings, tail one spring loaded. Pretty much same than Quorn type grinder, GREAT BOOK BTW.http://s164.photobucket.com/user/rtgeorge_album/media/broadley.gif.html

Went on swap meet this week-end. There was a guy with spindles, but they were massive. Mainly used in wood working machines ISO40 and one 1/3 of that but something like 30 mm bearing shaft and the AC-bearings were shot.

I have two open issues:

1: Grinding wheel type/spesification? I never have used grinding wheel to cast iron, but talked to few guys who did a little and lit looks like aluminium oxide abrasive (White....) and fairly coarse like 46 and bit open/friable would be worth of trying. looks like I have to settle on normal disc type wheel, dress it somewhat slant to negotiate around dovetails and that must do.

I could buy russian boron nitride small sharpening wheels, but they are cup or saucer type. Problem is that they are very fine, mostly 80-100, very few #60. Would that work "kissing" on cast iron?

2: I'm considering gluing the fixed front bearing on bearing housing. It is one part bearing (no adjustable preload). It would make nose of the spindle whole lot more easy and more compact.

I checked some ready made spindles and they are great for something a little larger. I'm in a hunt of something like dumore tool post grinder size.

Last weekend went on my daughte's graduation (primary->seconday) and showeling/wheel barrowing few tons of gravel around my front yard....no swarf was being produced, but looks like I have all the necessary steel to make spindle looking object.

I have been having a clear out and an Arrand spindle has surfaced - I've had it donkeys years but it is brand new in its box complete with two MT adaptors, a drive pulley and even the belt and belt joiner to drive it.

Andrew, That looks about right size and all (providing that cutting mat has metric graduation, not imperial). I remmember that brand poping up in UK mags -90s.

Is it made for grinding or does it has other uses? The draw bolt on taper hints for milling. Is that MT taper or something special? Need to device something to clamp the grinding stone and 180 mm dia, 20-25 mm width seems to calculate close to keep all simple.

Bearings might need changing, it's probably imperial?....but bearing boys is as close to me than it is to you.

Looks about right. Care to take aproximate lenght and width, by eyeballing is not calibrated.

Andrew, That looks about right size and all (providing that cutting mat has metric graduation, not imperial).......Pekka

Pekka,

I think they're 10mm squares on the cutting mat - some pictures show where the corner of an A4 and an A5 page would go; they are a little bit more than 6 squares apart in one direction, and about 8¾ squares in the other direction - so I reckon that's a pretty close match for 10 mm squares as A4 is 210 x 297 mm, A5 is 148 x 210 mm which would be 62mm difference x 87mm